Sending messages to other users on the Linux command line can be very easy, but there are a number of commands that you might want to consider. In this post, we’ll look at four commands and see how each of them works.
The wall command (as in "write all") allows you to send a message to all users who are currently logged into the system. This implies that the system is likely a server and that users are working on the command line. While the wall command is generally used by sysadmins to send out notices to users to let send out information (e.g., that the server is going down for maintenance), it can be used by any user.
Thanks to Sandra Henry-Stocker (see source)